Code review comment for lp:~pbeaman/akiban-persistit/tree-visitor-prototype

Sorry for the review slowness.

There is extremely little to actually do the visitor -- nice!

However, I'm not so sure that all the methods on ReadOnlyExchange are "safe". They are truly read only, but they do modify internal state. A nested traverse, due to calling one of the has* methods, would bork the _spareKey1, I think.

My only other nit is that the ReadOnlyExchange is an interface so the abstract clauses on each method are superfluous. Persistit has interface styles with both, but my 'druthers would be new ones without.